Create a 'returning visitor' or 'new visitor' property for Mixpanel.

returning-visitor.js

/**
 * If the mixpanel cookie exists this user was in the site before,
 * we have to consider him returning, only every 24 hours, just like GA.
 */
var RETURNING_VISITOR = document.cookie.indexOf('_mixpanel') != -1;
// if the mixpanel cookie does not exists the user is considered new
if (!RETURNING_VISITOR) {
  $.cookie('mp_visitor', true, { expires: 1, path: '/' });
// else the user might not be returning.
} else if ($.cookie('mp_visitor') !== null) {
  RETURNING_VISITOR = false;
}